Abstract: Method for retrieving data from a database, while assuring privacy, which comprises providing a database address for the data sought to be retrieved, generating at least two messages and communicating them to two or more database copies, generating two replies from the database copies, wherein one or more of said messages depends on the database address, a pseudo random or random number and wherein each reply depends on the message transmitted to the specific database copy, and the retrieved data is calculated as a function of said replies.

Abstract: An efficient software protection scheme is presented in which a data processing system provides comprehensive software protection using hardware and software measures. Specifically, it provides protection of the pattern of access to memory during execution of a program and also provides protection of the data stored in memory. The protection scheme is secure in the sense that it behaves like a black box which reveals no information other than the I/O behavior and running time. Thus, not only the values stored in the general purpose memory are hidden, but also the sequence in which memory location are accessed during execution is hidden. This comprehensive scope of protection is achieved by an extremely efficient scheme. In particular, if the running time of the original program it T, the running time of the protected program is only slower by some factor of (logT).sup.C where C is a small constant.

Abstract: A method for "on-line/off-line" digital signing is described and begins by pre-computing a data string x from a pair of matching public and secret keys of a digital signature scheme such that, for any message m later selected to be signed, a signature of m derived from x can be computed substantially faster than the signature of m derived from the matching public and secret keys. After a message m is selected to be signed, the method computes a signature .sigma. of the message m using the data string x. Because the method uses a two-stage approach to sign a message, the technique can be advantageously used to enhance the security of known digital signature schemes or to effect transaction processing using "smart" cards.